Apparatus for the recording of slow processes



Oct. 15, 1946. R'o'sA ET'AL.

APPARATUS FOR THE-RECORDING OF SLOW PROCESSES Filed Feb. 21; 1940 INVENTORS Laszlo 208a lmrc Zak areas Patented Oct. 15, 1946 APPARATUS FOR THE RECORDING OF SLOW PROCESSES Laszlo Rosa, Budapest VIII, and Imre Zakarias, Budapest VII, Hungary; vested in the Alien Property Custodian Application February 21, 1940, Serial No. 320,074 In Hungary February 11, 1939 4 Claims. (o1.12s-2.0e)

So called electro-cardiographs for the pick-up and recording of the cardiac function are already known, in which the electric voltage impulses induced by the work of the muscles of the heart are transferred on the luminous screen of a cathode ray tube or on an electro-mechanical device e. g. on a galvanometer, and in which the variation as a function of time of the voltages is traced on a film band kept in uniform motion. In View of the fact that in electrocardiography the peak values of the differences of potential between the electrodes do not amount to more than to about 2-3 millivolts, an amplifying apparatus comprising a number of stages is required in order to enable these voltage impulses to operate the recording device which possesses a relatively low degree of sensitivity. In the equipments of known types the necessary supply of heating and anode current is supplied by batteries forming part of the equipment. A drawback of this arrangement is that owing to the rapid diminution of voltages possible in the case of these batteries the amplification is, immediately after putting the apparatus in circuit, exposed to fluctuations, by which recording is rendered unreliable, the voltage condition of the batteries themselves being in general unknown to the attendants. Experiments have shown that it is possible to avoid the fluctuations of amplification if the voltages required forfeeding the amplifier tubes are derived from the electric mains system (if necessary from a motor-car storage battery) and if for stabilizing the anode and grid direct voltages of at least the first (input) amplifier tube at least two mutually consecutive filtering stages having high time constant are employed, at least one filtering stage consisting of a voltage-stabilizing tube or tubes, Whilst the remaining filtering stages either consist of a voltage stabilizing tube or tubes likewise, or of a voltage-stabilizing transformer, a motorgenerator having a sufficient degree of inertia, or a circuit arrangement comprising electronic tubes, e. g. a reflex circuit arrangement of stabilizer tubes.

The diagram of connections of an embodiment shown by way of example of the apparatus according to the invention is represented on the accompanying drawing. On the drawing, l denotes the first (input) amplifier tube, without the device for heating the cathode, whilst M denotes the second and I5 the third amplifier tube. As, in the case of apparatus for examining the cardiac function, it is essential that the fluctuations of the feeding voltages, expressed for the control grid of the first amplifier tube, should be smaller than 0.03 millivolt, a tube having a high degree of amplification, corresponding to an amplification factor g 33 preferably a screen grid tube is employed in the first amplifier stage. The voltage to be amplified which is admitted to the apparatus through the terminals II is impressed through the condenser 3 on the control grid 2 of this tube. The bias voltage of the control grid 2 is supplied by the battery 5 by means of the resistance 4. The feeding voltage for the anode 9 and for the screen grid 8 of the amplifier tube I is stabilized in the first stage by the series resistance l3 and by the four-stage stabilizer tube l0, whilst the second stage of stabilization is attended to by the stabilizer tubes 5 and l and by the series resistance it. The stabilizer tubes may be of the well known glow discharge type, such as neon tubes, which provide substantially a fixed voltage drop thereacross. The four-stage stabilizer tube 10 may comprise four of the tubes shown at 6 and I in series so as to break up the voltage drop across the tubes into stages. An example of a twostage stabilizer tube device is illustrated at H! in Fig. 4 of British Patent No. 472,951, accepted October 4, 1937. The current consumption of the stabilizer tube if! in the first filtering stage is higher (amounting to about 30-50 milliamperes) than the current consumption of the stabilizer tubes 6 and l of the second filtering stage (amount to about 5-10 milliamperes), which circumstance preferably also finds expression in the dimensions of the tubes in question. The stabilizer tubes 6 and 1 employed in the second filtering stage may possibly be dispensed with, and in the remaining filtering stages it is possible to employ voltage stabilizing transformers, circuit arrangements comprising electronic tubes e. g. refiex circuit arrangements of stabilizer tubes or motor generators possessing an adequate amount of mechanical inertia, the feeding of the lastnamed apparatus being effected by means of the alternating or direct current mains system or possibly by means of a motor car storage battery ofin which formula AEgz is the fluctuation of the cuit, which latter is marked ii on the drawing. f

In order to enable the compensation described above of the voltage fluctuations to be'achieved, the anode resistance H is constructed as an adjustable resistance. The calculation shows that in the case of the usual high-frequency pentodes the working resistance has to be adjusted between 50,000 and 100,000 ohms, in order to achieve compensation.

In the second amplifier stage the screen grid tube 14, and, respectively, in the third amplifier stage the triode I5 work with voltages stabilized in one stage only, the said stabilization being taken care of by the stabilizer tube i and by the series resistance :13. The anode resistance iii of the screen grid tube i4 is adjustable likewise, in the same way as the anode resistance 5 i in the first amplifier stage in order to enable the working point of the amplifier tube i l to be adjusted in such a manner as to ensure that the fiuctuations of the feeding voltages of the anode and of the screen grid, respectively, should just exactly mutually balance. The control grid 49 of the amplifier tube i i receives the bias voltage from the battery [3 over the resistance H. The feeding voltages for the anode 21 and for the screen grid of the amplifier tube M are stabilized by means of the stabilizer tub-e it and the series resistance I3. The control grid 2% of the triode l5 receives the bias voltage from the battery 3% over the resistance 30, whilst the control voltage itself is admitted to the control grid 2 through the condenser 32. The anode 33 works on the resistance 34, whilst the amplified voltage is admitted to the recording device e. g. cathode ray tube 36 at the terminals O-O by means of the condenser 35.

The condensers 22, 23, 2d, 21 and 28 as well as the resistance 25 and the switch 26 are employed for influencing the width of, i. e. for altering, the band of frequencies passed by the amplifier composed of the tubes l, I4, l5, and of the elements of circuit arrangement belonging to them. It is possible to assure by these means that the amplifier should pass those frequencies only, which are essential, e. g., in the recording of the cardiac function, the frequencies of the heart sound: 20

to 400 Hertz, and the frequencies of the electro- 1 cardiogram: 0.5 to 10 Hertz.

Experiments have shown that at least by way of first amplifier tube and of stabilizer tubes it is necessary to employ tubes of such a kind the essential electrodes of which are constructed as low in microphony as possible and/ or to fix these tubes in a resilient manner. The anode and grid bias voltages of the amplifier tubes in the second and further amplifier stages should be stabilized at least in one stage by means of low-frequency filtering with the aid of stabilizer tubes, it being possible to employ, partly or entirely, the same stabilizer tube or tubes for the stabilizing of the feeding voltages of the various amplifier stages. The control grid bias voltage of the amplifier tubes can be produced by means of the voltage drop in one cathode resistance, or supplied from; a stabilized voltage; the bias voltage of the first amplifier tube and possibly also those of further amplifier tubes should preferably be taken from a battery, possibly by means of a voltage divider of high resistance.

For the calibration of the amplifier it is possible to derive alternating voltage, preferably by means of a resistive voltage divider, from the heating voltage of the amplifier tubes, it being possible to impress the said calibrating voltage on the control grid of the first amplifier tube.

If in the apparatus, recording is effected by means of a cathode ray tube, it is preferable to employ a cathode ray tube of such a type the fluorescent screen of which emits blue light for the purposes of taking photographs, and green, yellow or white light for the purposes of direct observation, or in which a secondary luminous surface is employed. As the inertia of the human eye amounts to about one-eighth of one second, the time constant of the luminous substance emitting the green, yellow or white light should be greater than one-third of one second. The voltage to be graphically recorded is impressed upon one of the pairs of deflecting plates of the cathode ray tube, whilst in the case of direct observation a saw-tooth voltage is impressed on the other pair of deflecting plates, the frequency of which saw-tooth voltage can be synchronized with that of the heart-beat. As the period of one heart-beat may vary between about 0.2 and 2 seconds, the saw-tooth voltage generator should be constructed in such a manher as to enable the period of oscillation to be adjusted at least between 0.5 and 2 seconds. The capacity of the condenser, periodically charged and discharged for producing the saw-tooth voltage should be assumed at a value higher than 2 micro-farads.

In the case of an electrocardiographic examination, for instance, the apparatus should be used in the following manner: The electrodes fixed to the right and left arms of the person to be examined should be connected to the terminals II. The difference of potential produced by the cardiac function should be amplified by means of the tubes I, It, I5; the amplified voltage should be taken off at the terminals OO and may be supplied, e. g., to one pair of deflecting plates of a cathode ray tube, from which the variation in time of the difference of potential, i. e., the so-called electrocardiogram should be photographed on a running film band.

What we claim is:

1. Apparatus for the pick-up and recording of slow processes of motion taking place in organs of the human or animal body, especially of the function of the heart, the said apparatus consisting of a recording device, of an amplifier, of a common power source for the feeding of the amplifier tubes, and of stabilizing means for the anode and grid direct voltages of at least the first (input) amplifier tube, said stabilizing means consisting of at least two consecutive filtering stages having high time constants, each of the said filtering stages consisting of a voltage stabilizing tube device, the current dissipation and preferably also the dimensions of the voltage stabilizing tube device of the first stage being greater than the current dissipation and dimensions of the voltage stabilizing tube device of the second filtering stage.

2. Apparatus for the pick-up and recording of slow processes of motion taking place in organs of the human or animal body, especially of the function of the heart, the said apparatus consessing a high amplification factor greater than 5 33, for the adjustment of the working point whereof a variable resistanc is provided, and of stabilizing means for the anode and grid direct. voltages of at least the first (input) amplifier tube, said stabilizing means consisting of at least 10 two consecutive filtering stages having high time constants, each of the said filtering stages consisting of a voltage stabilizing tube device, the" current dissipation and the dimensions of the voltage stabilizing tub device of the first stage 15 being greater than the current dissipation and dimensions of the voltage stabilizing tube device of the second filtering stage.

3. Apparatus for the pick-up and recording of slow processes of motion taking place in organs 20 of the human or animal body, especially of the function of the heart, the said apparatus con sisting of a recording device, of an amplifier, of a common power source for the feeding of the amplifier tubes and of at least one filtering member serving for the adjustment in the desired extent of the band of frequencies passed by the amplifier, each filtering member being composed of a condenser and a resistance, and of stabilizing means for the anode and grid direct voltages of atleast the first (input) amplifier tube, said stabilizin means consisting of at least two consecutive filtering stages having high time constants, each of the said filtering stages consisting of a voltage stabilizing tube device, the current dissipation and the dimensions of the voltage stabilizing tube device of the first stage being greater than the current dissipation and dimensions of the voltage stabilizing tube device of the second filtering stage.

4. The apparatus of claim 1 including a screen grid and an anode in said first amplifier tube, and a resistance in. series with said anode of the order of 50,000 ohms whereby fluctuations of the anode and screen grid voltages substantially neutralize each other.

LASZLO ROSA. IMRE ZAKARIAS. 

